Optical recording media made of binary antimony-tin alloy have relatively low amorphous-to-crystalline transition temperatures and hence, are not suitable for applications where severe temperature conditions are to be expected. Further, the carrier-to-noise ratio is about 55 dB for the binary alloy. This is adequate for most applications, but improvement is desirable for more demanding ones.
Indium can be used to stabilize the amorphous phase of the SbSn alloy by increasing the amorphous to crystalline transition temperature. Indium was first selected since its atomic number (49) is similar to that of antimony (51) and tin (50). The use of indium also results in a significant improvement in the carrier-to-noise ratio of the recording process.
Subsequent to the discovery that indium could be used to improve the properties of the antimony-tin alloy, other antimony-tin based alloys were discovered by the present assignee. Thus, applications were filed on antimony-tin alloys containing aluminum (U.S. Pat. No. 4,798,785); zinc (U.S. Pat. No. 4,774,170); and germanium (U.S. Pat. No. 4,795,695).
U.S. Pat. No. 4,981,772 discloses a method of recording using a write-once amorphous alloy layer of SbSnO. While this alloy exhibited a higher amorphous to crystalline transition temperature over the prior art, still further improvement is desirable.